IndietroMicrobiology Chapter 2
Termini in questo insieme (116)
Why is the cytoplasmic membrane amphipathic?
It contains hydrophilic (water-loving) heads and hydrophobic (water-fearing) tails
What makes up the hydrophilic head of a bacterial phospholipid?
Fatty acid tails
What type of linkage is found in bacterial membrane lipids?
Ester linkages
What type of linkage is found in archaeal membrane lipids?
Ether linkages
How do the hydrophobic tails of Bacteria and Archaea differ?
Bacteria have fatty acid tails; Archaea have isoprenoid tails
What membrane arrangements can Archaea have?
A lipid bilayer, monolayer, or a mixture of both
What are the main functions of the cytoplasmic membrane?
Permeability barrier, protein anchor, and energy conservation/consumption
What does the cytoplasmic membrane do as a permeability barrier?
Controls transport of molecules; polar and charged molecules must be transported across it
What does the cytoplasmic membrane do as a protein anchor?
Holds proteins in place
How is the cytoplasmic membrane involved in energy conservation?
It generates the proton motive force (PMF)
What is active transport?
Accumulation of solutes against the concentration gradient using energy
What energy source does simple transport use?
Proton motive force (PMF)
How many transport proteins are required for simple transport?
One transmembrane transport protein
What is symport?
The solute and H+ are transported in the same direction
What is antiport?
The solute and H+ are transported in opposite directions?
What is group translocation?
Transport in which the substance being transported is chemically modified
What is the best-studied group translocation system?
The phosphotransferase system (PTS)
What provides energy for the phosphotransferase system?
Phosphoenolpyruvate (PEP) from glycolysis
How many proteins are required by the phosphotransferase system?
Five proteins
What happens to a solute during transport by the phosphotransferase system?
It is chemically modified
What provides energy for ABC transporters?
ATP
What three components make up an ABC transporter?
Binding protein, transmembrane transporter, and ATP-hydrolyzing protein
What is the energy source of simple transport vs PTS vs ABC transport?
Simple transport: PMF
PTS: PEP
ABC transport: ATP
What is the number of proteins/components required for simple transport vs PTS vs ABC transport?
Simple transport: 1 transmembrane protein
PTS: 5 proteins
ABC transport: 3 components
What is peptidoglycan?
A rigid polysaccharide layer that provides strength to bacterial cell walls
How does the bacterial cell wall provide rigidity and structure?
It withstands osmotic/turgor pressure, prevents cell lysis, and maintains cell shape and rigidity
What two sugars make up the peptidoglycan backbone?
N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
What type of linkage connects NAG and NAM in peptidoglycan?
β-1,4 linkages
What is attached to NAM in peptidoglycan?
A short peptide
What structures make up the Gram-positive cell envelope?
Cytoplasmic membrane + thick cell wall
What structures make up the Gram-negative cell envelope?
Cytoplasmic membrane + thin cell wall + outer membrane + periplasm
How does peptidoglycan thickness differ between Gram-positive and Gram-negative bacteria?
Gram-positive has thick peptidoglycan; Gram-negative has thin peptidoglycan
What acids are characteristic of Gram-positive cell walls?
Teichoic acids and lipoteichoic acids
What structure is found in Gram-negative but not Gram-positive cell envelopes?
An outer membrane containing LPS
What is the periplasm?
The space between the cytoplasmic and outer membranes of Gram-negative bacteria
How does lysozyme affect peptidoglycan?
It cleaves the glycosidic bond between the NAG and NAM sugars, destroying preexisting peptidogylcan
How does penicillin affect peptidoglycan?
It blocks formation of peptide cross-links, leading to cell lysis
Why are Archaea different from Bacteria in their response to agents that target peptidoglycan?
Archaeal cell walls lack peptidoglycan
What is LPS and where is it found?
Lipopolysaccharide, found in the outer membrane of Gram-negative bacteria
What part of the LPS has endotoxin properties?
Lipid A
What is endotoxin?
The toxic component of LPS
What is an S-layer?
A paracrystalline protein/glycoprotein structure that forms the outermost layer of the cell envelope
What are the functions of an S-layer?
Provides strength and shape, protects against lysis and host defenses, and facilitates surface interactions/adhesion
What alternative cell envelope arrangements are listed? (Uncommon but possible)
S-layers around Gram-positive or Gram-negative bacteria; Archaea with only an S-layer; archaeal pseudomurein walls with or without an S-layer; Archaea with an outer membrane; and wall-less Bacteria or Archaea with tough cytoplasmic membranes
What bacterial and archaeal examples lack cell walls?
Mycoplasma (Bacteria) and Thermoplasma (Archaea)
What are pili?
Thin, filamentous protein structures that allow organisms to attach to surfaces or form pellicles and biofilms
What are fimbriae?
Numerous, short pili that mediate attachment
How do fimbriae and pili compare in structure and function?
Both are filamentous protein structures involved in attachment; fimbriae are numerous, short pili specialized for attachment
What are conjugative pili used for?
Conjugation, the direct transfer of genetic material between cells
What are electrically conductive pili (nanowires) used for?
Conducting electrons toward or away from the cell; they play a role in energy metabolism
What are Type IV pili used for?
Twitching motility and colonization
What are the major functions of cell inclusions?
They serve as energy reserves, carbon or phosphorus reservoirs, or perform special functions
What is PHB?
The most common carbon storage polymer
When are PHAs synthesized and what is their purpose?
They are synthesized when carbon is in excess and serve as a carbon or energy source
What is the function of glycogen inclusions?
They store carbon and energy and are produced when carbon is in excess
When do polyphosphate granules form?
When phosphate is in excess
What is the purpose of polyphosphate granules?
They provide phosphate for nucleic acid and phospholipid biosynthesis when phosphate becomes limiting
What is an endospore?
A highly differentiated, dormant survival structure (not a reproductive cell)
What conditions can endospores survive?
Extreme heat, radiation, chemical exposure, drought, and nutrient loss
What bacterial genera form from endospores?
Bacillus and Clostridium
What triggers sporulation?
Limiting nutrients
What triggers endospore germination?
Nutrient availability
How do endospores differ from vegetative cells in resistance?
Endospores have high resistance to heat, radiation, chemicals, and lysozyme; vegetative cells have low resistance and are lysozyme-sensitive
How does water content differ between an endospore and vegetative cell?
Vegetative cell: 80-90% water
Endospore core: 10-25% water
What substances are present in endospores but absent in vegetative cells?
Dipicolinic acid and small acid-soluble spore proteins (SASPs)
Why can endospore-forming bacteria create problems for human health or the food industry?
Their endospores are highly resistant to heat, radiation, chemicals, drought, and nutrient loss, allowing them to survive harsh conditions
What is the function of bacterial flagella and archaeal archaella?
Swimming motility
What are the main parts of a bacterial flagellum?
Filament, hook, and basal body (motor)
What powers bacterial flagellar rotation?
Proton motive force
What powers archaella?
ATP hydrolysis
How do archaella structurally differ from bacterial flagella?
Archaella are smaller, their proteins are unrelated to bacterial flagella, and they are more closely related to Type IV pili
What is a polar flagellar arrangement?
Flagella attached at one end or both ends of the cell
What is a lophotrichous arrangement?
A tuft of flagella at one end
What is a peritrichous arrangement?
Flagella located around the cell surface
How do eukaryotic flagella move?
By a whip-like motion
What is the structural arrangement of eukaryotic flagella?
Nine pairs of microtubules surrounding a central pair
What protein and energy source power eukaryotic flagella?
Dynein using ATP
How do prokaryotic and eukaryotic flagella differ in movement?
Bacterial flagella rotate, while eukaryotic flagella use a whip-like motion
How do bacterial and eukaryotic flagella differ in energy source?
Bacterial flagella use PMF; eukaryotic flagella use ATP
What structure is required for twitching motility?
Type IV pili
How does twitching motility move a cell?
Pili extend from one pole, attach to a surface, then retract to pull the cell forward
What powers twitching motility?
ATP hydrolysis
What is gliding motility?
Smooth, continuous movement along the cell's long axis without external structures
What powers gliding motility?
Proton motive force
What is taxis?
Directed movement in response to chemical or physical stimuli
What is chemotaxis?
Movement in response to chemicals
What is phototaxis?
Movement in response to light
What is aerotaxis?
Movement in response to oxygen
What is osmotaxis?
Movement in response to ionic strength
What is hydrotaxis?
Movement in response to water
What is a capillary tube assay used to measure?
Chemotaxis
How is a capillary tube assay performed?
A capillary containing an attractant or repellant is inserted into a suspension of motile bacteria
What happens when bacteria are attracted to the chemical in a capillary tube?
They swarm toward the attractant, increasing the number of cells in the capillary
Why is a control lacking attractant needed in a capillary tube assay?
It provides a comparison to determine whether increased bacterial accumulation is due to the attractant rather than simply entry into the capillary
What is the result of mitosis?
Two diploid daughter cells with no genetic diversity
What is the result of meiosis?
Four haploid gametes with genetic diversity
What happens to chromosome number during meiosis?
Meiosis converts diploid cells into haploid cells
What is the function of the nucleus?
It contains the chromosomes (DNA)
What is the function of the nucleolus?
Site of rRNA synthesis and where ribosomal subunits begin development
What is the major function of mitochondria?
Respiration and oxidative phosphorylation for aerobic eukaryotes
What are cristae?
Folded internal mitochondrial matrix
What is found in the mitochondrial matrix?
Citric acid cycle enzymes
What is the function of the rough ER?
Produces glycoproteins and new membrane material
What is the function of the smooth ER?
Lipid synthesis and carbohydrate metabolism
What is the function of the Golgi complex?
Modifies ER products
What is the function of lysosomes?
Contain digestive enzymes and recycle cell components through degradation
What is the major function of chloroplasts?
They specialize in energy metabolism in phototrophs; thylakoids contain chlorophyll and ATP-synthetic components, and the stroma contains RuBisCO for converting CO2 to organic compounds
What three structural elements make up the eukaryotic cytoskeleton?
Microtubules, microfilaments, and intermediate filaments
What are microtubules made of and what do they do?
Hollow tubes of α- and β-tubulin that maintain cell shape, facilitate motility, and move chromosomes during mitosis
What are microfilaments made of and what do they do?
Actin polymers that maintain/change cell shape and function in amoeboid motility and cell division
What do intermediate filaments do?
Maintain cell shape and position organelles
What does the endosymbiotic theory propose?
Mitochondria and chloroplasts were originally prokaryotes
What DNA and ribosome evidence supports the endosymbiotic theory?
Mitochondria and chloroplasts have their own circular DNA and 70S ribosomes, similar to bacteria
What structural evidence supports the endosymbiotic theory?
Mitochondria and chloroplasts have double membranes and are similar in size to bacteria
What reproductive evidence supports the endosymbiotic theory?
They replicate by a process similar to binary fission
What genetic evidence supports the endosymbiotic theory?
They contain genes resembling certain bacterial genes